1. Field of the Invention
The present invention concerns a method for acquisition of magnetic resonance slice images of an examination subject of a patient by means of a magnetic resonance apparatus having a control device controlling the image acquisition operation, whereby the slice images being acquired as slice image stacks situated in different planes in a field of view within a homogeneous magnetic field.
2. Description of the Prior Art
Slice images of an examination subject of a patient can be acquired in high-resolution form by a magnetic resonance apparatus. The patient is exposed to a homogeneous magnetic field. Further radio-frequency magnetic field, namely gradient fields that serve for spatial resolution, and a radio-frequency field, causing magnetic resonance signals to be generated in the examination subject that are detected and used for image generation. The basic manner of operation of such a magnetic resonance apparatus is well known and need not be described in more detail herein.
Magnetic resonance data from an examination subject are typically acquired in the form of a number of individual slice images. These slice images lie atop one another in different levels, frequently separated by a very narrow gap; thus consequently with a defined separation. The slice images themselves, which are aligned with regard to a specific anatomical structure, typically lie parallel to one another. Such a slice image stack thus provides image information from various levels of the examination subject. A total image of an examination subject is typically acquired with a previously-defined number of individual slice images, the slice thickness and the possibly-defined gap being also set in advance. In brain acquisitions, 19 individual slice images are acquired; the slice thickness is, for example, 10 mm with a gap of 1 mm. Such acquisition parameters are frequently set in advance for a brain acquisition. Corresponding parameter sets also exist for acquisition of other examination regions, such as organs or bones or the like.
The size of the examination subject frequently varies considerably dependent on the patient size. The brain of a small child is distinctly smaller than that of an adult; bone structures (for example joint or innominate bones) vary significantly in their size from child to adult. If (with regard to the example of a brain acquisition) the brain of an small child is examined with the same slice count, the same slice thickness and the same gap as the parameters are defined for the brain acquisition of an adult, some slices will inevitably no longer measure in the brain but rather outside of the brain. This image information consequently does not contribute to the imaging of the actual examination subject. In reverse, if the brain of an adult is acquired starting from the parameters relating to the size of the child's brain, the entire brain inevitably will not be imaged since this is distinctly larger than the child's brain, for which optimal coverage requires the acquisition parameters to be defined. The acquisition of a brain is only an example. These problems result in equal measure given the acquisition of other examination subjects where considerable size differences are present, in particular, for example, in the acquisition of structures (such as the bones) varying significantly as a result of growth.
In order to address this problem, the operator of a magnetic resonance data acquisition apparatus has previously been required to manually set the slice thickness and/or the slice interval (gap) (typically starting from an unchanged slice count) in order to define an optimal slice coverage with regard to the real size of the examination subject. The slice count is typically retained since as few parameters as possible are changed by the operator for adaptation to the examination subject and a high image count is desired. This manual adaptation is not only laborious and time-consuming but also possibly incorrect (such as in the case of a wrong parameter setting), such that the subsequent image acquisition is not usable or not completely usable.